GOA circuit based on LTPS semiconductor TFT

ABSTRACT

The present invention provides a GOA circuit based on LTPS semiconductor TFT, comprising a plurality of GOA units which are cascade connected, and N is set to be a positive integer and an Nth GOA unit comprises a pull-up control part ( 100 ), a pull-up part ( 200 ), a first pull-down part ( 400 ) and a pull-down holding part ( 500 ); the pull-down holding part ( 500 ) utilizes a high/low voltage reverse design and comprises a first, a second and a third DC constant low voltage levels (VSS 1 , VSS 2 , VSS 3 ) which are sequentially abated and a DC constant high voltage level (H), the influence of electrical property of the LTPS semiconductor TFT to the GOA driving circuit, and particularly the bad function due to the electric leakage issue can be solved; meanwhile, the existing issue that the second node voltage level the pull-down holding circuit part in the GOA circuit based on the LTPS semiconductor TFT cannot be at higher voltage level in the functioning period can be solved to effectively maintain the first node (Q(N)) and the output end (G(N)) at low voltage level.

FIELD OF THE INVENTION

The present invention relates to a display technology field, and moreparticularly to a GOA circuit based on LTPS semiconductor TFT.

BACKGROUND OF THE INVENTION

GOA (Gate Drive On Array) is to manufacture the gate driver on the arraysubstrate by utilizing the Thin Film Transistor (TFT) liquid crystaldisplay array process for achieving the driving method of scanning lineby line.

Generally, the GOA circuit comprises a pull-up part, a pull-upcontrolling part, a transfer part, a pull-down part, a pull-down holdingpart and a boost part in charge of boosting voltage level. The boostpart generally comprises a bootstrap capacitor.

The pull-up part is mainly in charge of outputting the inputted clocksignal (Clock) to the gate of the thin film transistor as being thedriving signals of the liquid crystal display. The pull-up control partis mainly in charge of activating the pull-up part, and is generallyfunctioned by the signal transferred from the former GOA circuit. Thepull-down part is mainly in charge of rapidly pulling down the scansignal (i.e. the voltage level of the gate of the thin film transistor)to be low voltage level after outputting the scanning signal. Thepull-down holding circuit part is mainly in charge of maintaining thescanning signal and the signal of the pull-up part in an off state (i.e.the set negative voltage level). The boost part in mainly in charge ofperforming a second boost to the voltage level of the pull-up part forensuring the normal output of the pull-up part.

With the development of the LTPS semiconductor TFT, the LTPS-TFT LCDalso becomes the focus that people pay lots of attentions. Because theLTPS semiconductor has better order than amorphous silicon (a-Si) andthe LTPS itself has extremely high carrier mobility which can be morethan 100 times of the amorphous silicon semiconductor, which the GOAskill can be utilized to manufacture the gate driver on the TFT arraysubstrate to achieve the objective of system integration and saving thespace and the cost of the driving IC. However, in prior arts, only fewdevelopments are proceeded for focusing on the GOA circuit of LTPSsemiconductor TFT. Particularly, many problems caused by the electricalproperty of the oxide thin film transistors themselves have to beovercome. For instance: threshold voltage is generally larger than 0V inthe electrical property of the traditional amorphous silicon thin filmtransistor and the swing of the subthreshold range voltage is relativelylarger than the electrical current. However, the threshold voltage ofthe LTPS semiconductor TFT is lower (about 0V in general) and thesubthreshold range swing is smaller. Many elements may function in astate of closing to the threshold voltage or even higher than thethreshold voltage when the GOA circuit is in off state. Accordingly, thedesign difficulty of a LTPS GOA circuit will be increased because of theelectrical leakage and working current drift of the TFTs in the circuit.Many designs which are adaptable to the scan driving circuit for theamorphous silicon semiconductors cannot be easily applied to the linescan driving circuit of LTPS semiconductor. Some function issues willexist which can directly result in malfunction of the LTPS GOA circuit.Therefore, the influence of the LTPS semiconductor TFT properties to theGOA circuit has to be considered as designing the circuit.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a GOA circuit basedon LTPS semiconductor TFT to solve the influence of electrical propertyof the LTPS semiconductor TFT to the GOA driving circuit, andparticularly the bad function due to the electric leakage issue; theissue that the second node voltage level and the pull-down holdingcircuit part in the GOA circuit based on the LTPS semiconductor TFTcannot be at higher voltage level in the non-functioning period can besolved.

For realizing the aforesaid objective, the present invention provides aGOA circuit based on LTPS semiconductor TFT, comprising a plurality ofGOA units which are cascade connected, and N is set to be a positiveinteger and an Nth GOA unit comprises a pull-up control part, a pull-uppart, a first pull-down part and a pull-down holding part;

the pull-up control part comprises a first transistor, and both a gateand a source thereof are electrically coupled to an output end of anN−1th GOA unit which is the former stage of the Nth GOA unit, and adrain is electrically coupled to a first node;

the pull-up part comprises a second transistor, and a gate thereof iselectrically coupled to the first node, and a source is electricallycoupled to a first clock driving signal, and a drain is electricallycoupled to an output end;

the pull-down holding part is electrically coupled to the first node,the output end, a DC constant high voltage level, and a first, a secondand a third DC constant low voltage levels;

the pull-down holding part utilizes a high/low voltage reverse designand comprises:

a third transistor, and both a gate and a source of the third transistorare electrically coupled to the DC constant high voltage level, and adrain is electrically coupled to a source of a fifth transistor;

a fourth transistor, and a gate of the fourth transistor is electricallycoupled to the drain of the third transistor, and a source iselectrically coupled to the DC constant high voltage level, and a drainis electrically coupled to a second node;

the fifth transistor, and a gate of the fifth transistor is electricallycoupled to the first node, and the source is electrically coupled to thedrain of the third transistor, and a drain is electrically coupled tothe first DC constant low voltage level;

a sixth transistor, and a gate of the sixth transistor is electricallycoupled to the first node, and a source is electrically coupled to thesecond node, and a drain is electrically coupled to a source of aneighth transistor;

the eighth transistor, and the gate of the eighth transistor iselectrically coupled to the first node, and the source is electricallycoupled to the drain of the sixth transistor, and a drain iselectrically coupled to the third DC constant low voltage level;

the tenth transistor, and the gate of the tenth transistor iselectrically coupled to the second node and a source is electricallycoupled to the DC constant high voltage level, and a drain iselectrically coupled to the drain of the sixth transistor;

a twelfth transistor, and a gate of the twelfth transistor iselectrically coupled to the second node, and a source is electricallycoupled to the first node, and a drain is electrically coupled to thesecond DC constant low voltage level;

a thirteenth transistor, and a gate of the thirteenth transistor iselectrically coupled to the second node, and a source is electricallycoupled to the output end, and a drain is electrically coupled to thefirst DC constant low voltage level;

the third transistor, the fourth transistor, the fifth transistor, thesixth transistor provide positive high voltage levels, employed tocontrol activations of the twelfth transistor and the thirteenthtransistor; the eighth transistor constructs a reverse bootstrap ofnegative voltage level in a functioning period, employed to provide alower voltage level to the second node in the functioning period; the DCconstant high voltage level is utilized to provide a proper high voltagelevel to the second node in a non-functioning period to maintain thefirst node and the output end at low voltage level;

the first pull-down part is electrically coupled to the first node, asecond clock driving signal and the second DC constant low voltagelevel, and the pull-down part pulls down a voltage level of the firstnode to the second DC constant low voltage level according to the secondclock driving signal;

the first pull-down part comprises a fourteenth transistor, and a gateof the fourteenth transistor is electrically coupled to the second clockdriving signal, and a source is electrically coupled to the first node,and a drain is electrically coupled to the second DC constant lowvoltage level;

the third DC constant low voltage level<the second DC constant lowvoltage level<the first DC constant low voltage level.

The pull-down holding part further comprises a ninth transistor, and agate of the ninth transistor is coupled to the first node, and a sourceis electrically coupled to the gate of the tenth transistor, and a drainis electrically coupled to the third DC constant low voltage level; aneleventh transistor, and both a gate and a source of the eleventhtransistor are electrically coupled to the DC constant high voltagelevel, and a drain is electrically coupled to the gate of the tenthtransistor; the gate of the tenth transistor is disconnected with thesecond node.

The fourth transistor, the sixth transistor and the eighth transistorare coupled in series.

The GOA circuit based on LTPS semiconductor TFT further comprises aboost part, and the boost part is electrically coupled between the firstnode and the output end, employed to boost voltage level of the firstnode.

The boost part comprises a capacitor, and one end of the capacitor iselectrically coupled to the first node, and the other end iselectrically coupled to the output end.

Waveform duty ratios of the first clock driving signal and the secondclock driving signal are smaller than 50/50; the fourteenth transistorpulls down the voltage level of the first node to the second DC constantlow voltage level in a high voltage level period of the second clockdriving signal.

A signal output waveform of the first node changes according to thevariation of the waveform duty ratios of the first clock driving signaland the second clock driving signal.

The signal output waveform of the first node appears to be convex.

In the first level connection of the GOA circuit, both the gate and thedrain of the first transistor are electrically coupled to an activationsignal end of the circuit.

The GOA circuit employs an output signal of the output end as being aformer-latter level transfer signal.

The benefits of the present invention are: in the GOA circuit based onLTPS semiconductor TFT, the pull-down holding part utilizes a high/lowvoltage reverse design and comprises a first, a second and a third DCconstant low voltage levels which are sequentially abated and a DCconstant high voltage level. The influence of electrical property of theLTPS semiconductor TFT to the GOA driving circuit, and particularly thebad function due to the electric leakage issue can be solved; meanwhile,the existing issue that the second node voltage level and the pull-downholding circuit part in the GOA circuit based on the LTPS semiconductorTFT cannot be at higher voltage level in the non-functioning period canbe solved to effectively maintain the first node and the output end atlow voltage level.

BRIEF DESCRIPTION OF THE DRAWINGS

For better explaining the technical solution and the effect of thepresent invention, the present invention will be further described indetail with the accompanying drawings in the specific embodiments.

In drawings,

FIG. 1 is a circuit diagram of a GOA circuit based on LTPS semiconductorTFT according to the first embodiment of the present invention;

FIG. 2 is a circuit diagram of the first level connection of the GOAcircuit based on LTPS semiconductor TFT according to the firstembodiment of the present invention;

FIG. 3 is a circuit diagram of the GOA circuit based on LTPSsemiconductor TFT according to the second embodiment of the presentinvention;

FIG. 4 is an output waveform diagram of the first waveform settings andthe key nodes in a GOA circuit based on LTPS semiconductor TFT accordingto the present invention;

FIG. 5 is an output waveform diagram of the second waveform settings andthe key nodes in a GOA circuit based on LTPS semiconductor TFT accordingto the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

For better explaining the technical solution and the effect of thepresent invention, the present invention will be further described indetail with the accompanying drawings and the specific embodiments.

Please refer to FIGS. 1-2. The present invention provides a GOA circuitbased on LTPS semiconductor TFT. As shown in FIG. 1, the GOA circuitbased on LTPS semiconductor TFT comprises a plurality of GOA units whichare cascade connected, and N is set to be a positive integer and an NthGOA unit comprises a pull-up control part 100, a pull-up part 200, afirst pull-down part 400 and a pull-down holding part 500; further aboost part 300.

The pull-up control part 100 comprises a first transistor T1, and both agate and a source of the first transistor T1 are electrically coupled toan output end G(N−1) of an N−1th GOA unit which is the former stage ofthe Nth GOA unit, and a drain is electrically coupled to a first nodeQ(N);

The pull-up part 200 comprises a second transistor T2, and a gatethereof is electrically coupled to the first node Q(N), and a source iselectrically coupled to a first clock driving signal CKN, and a drain iselectrically coupled to an output end G(N);

The boost part 300 comprises a capacitor Cb, and one end of thecapacitor Cb is electrically coupled to the first node Q(N), and theother end is electrically coupled to the output end G(N).

The pull-down holding part 500 is electrically coupled to the first nodeQ(N), the output end G(N), a DC constant high voltage level H, and afirst, a second and a third DC constant low voltage levels VSS1, VSS2,VSS3. Specifically, the pull-down holding part 500 comprises: a thirdtransistor T3, and both a gate and a source of the third transistor T3are electrically coupled to the DC constant high voltage level H, and adrain is electrically coupled to a source of a fifth transistor T5; afourth transistor T4, and a gate of the fourth transistor T4 iselectrically coupled to the drain of the third transistor T3, and asource is electrically coupled to the DC constant high voltage level H,and a drain is electrically coupled to a second node P(N); the fifthtransistor T5, and a gate of the fifth transistor T5 is electricallycoupled to the first node Q(N), and the source is electrically coupledto the drain of the third transistor T3, and a drain is electricallycoupled to the first DC constant low voltage level VSS1; a sixthtransistor T6, and a gate of the sixth transistor T6 is electricallycoupled to the first node Q(N), and a source is electrically coupled tothe second node P(N), and a drain is electrically coupled to a source ofan eighth transistor T8; the eighth transistor T8, and the gate of theeighth transistor T8 is electrically coupled to the first node Q(N), andthe source is electrically coupled to the drain of the sixth transistorT6, and a drain is electrically coupled to the third DC constant lowvoltage level VSS3; the tenth transistor T10, and the gate of the tenthtransistor T10 is electrically coupled to the second node P(N) and asource is electrically coupled to the DC constant high voltage level H,and a drain is electrically coupled to the drain of the sixth transistorT6; a twelfth transistor T12, and a gate of the twelfth transistor T12is electrically coupled to the second node P(N), and a drain iselectrically coupled to the first node Q(N), and a source iselectrically coupled to the second DC constant low voltage level VSS2; athirteenth transistor T13, and a gate of the thirteenth transistor T13is electrically coupled to the second node P(N), and a drain iselectrically coupled to the output end G(N), and a source iselectrically coupled to the first DC constant low voltage level VSS1.

The first pull-down part 400 comprises a fourteenth transistor T14, anda gate of the fourteenth transistor T14 is electrically coupled to thesecond clock driving signal XCKN, and a source is electrically coupledto the first node Q(N), and a drain is electrically coupled to thesecond DC constant low voltage level VSS2.

As shown in FIG. 2, in the first level connection of the GOA circuit,both the gate and the drain of the first transistor T1 are electricallycoupled to an activation signal end STV of the circuit.

Specifically, the GOA circuit based on LTPS semiconductor TFT accordingto the present invention comprises a DC constant high voltage level Hand three DC constant low voltage levels VSS1, VSS2, VSS3. The three DCconstant low voltage levels VSS1, VSS2, VSS3 are sequentially abated,i.e. the third DC constant low voltage level<the second DC constant lowvoltage level<the first DC constant low voltage level. The three DCconstant low voltage levels VSS1, VSS2, VSS3 are separately andindependently controlled for conveniently performing adjustments ofdifferent voltage levels.

The pull-down holding part 500 utilizes a high/low voltage reversedesign; the third transistor T3, the fourth transistor T4, the fifthtransistor T5, the sixth transistor T6 provide positive high voltagelevels, employed to control activations of the twelfth transistor T12and the thirteenth transistor T13; the eighth transistor T8 constructs areverse bootstrap of negative voltage level, employed to pull down thesecond node P(N) to the third DC constant low voltage level VSS3 in thefunctioning period; the DC constant high voltage level H is utilized toprovide a proper high voltage level to the second node P(N) in anon-functioning period to maintain the first node Q(N) and the outputend G(N) at low voltage level to eliminate the ripple of the two. Thefourth transistor T4, the sixth transistor T6 and the eighth transistorT8 are coupled in series which is capable of preventing electricalleakage. With the aforesaid arrangement of the pull-down holding part500, it is capable of reducing the amount of the TFTs and saving layout.Moreover, the gate of the tenth transistor T10 coupled to the secondnode P(N) can prevent the damage of the over high voltage level to thetenth transistor T10.

Specifically, the third transistor T3, the fourth transistor T4 of thepull-down holding part 500 is controlled by the DC constant high voltagelevel H to be in an activated state. In non-functioning period, thefifth transistor T5, the sixth transistor T6 are deactivated, and thefourth transistor T4 provides the DC constant high voltage level H tothe second node P(N). When the second node P(N) is at high voltagelevel, both the twelfth transistor T12, the thirteenth transistor T13are activated. The voltage level of the first node Q(N) is pulled downto the second DC constant low voltage level VSS2 by the twelfthtransistor T12. The voltage level of the output end G(N) is pulled downto the first DC constant low voltage level VSS1 by the thirteenthtransistor T13; in functioning period, the gates of the fifth transistorT5, the sixth transistor T6, the eighth transistor T8 are high voltagelevel transmitted from the first node Q(N), and all of the fifthtransistor T5, the sixth transistor T6, the eighth transistor T8 areactivated. The gate voltage of the fourth transistor T4 is pulled downto the first constant DC low voltage level VSS1 by the fifth transistorT5, and the fourth transistor T4 is deactivated and no longer providesthe DC constant high voltage level H to the second node P(N). Now, boththe sixth transistor T6 and the eighth transistor T8 are activated. Thevoltage level of the second node P(N) is pulled down to the third DCconstant low voltage level VSS3 which is lower by the sixth transistorT6 and the eighth transistor T8.

With the pull-down holding part 500 in cooperation with the DC constanthigh voltage level H and three DC constant low voltage levels VSS1,VSS2, VSS3, the influence of electrical property of the LTPSsemiconductor TFT to the GOA driving circuit, and particularly the badfunction due to the electric leakage issue can be solved; meanwhile, theexisting issue that the second node voltage level and the pull-downholding circuit part in the GOA circuit based on the LTPS semiconductorTFT cannot be at higher voltage level in the non-functioning period canbe solved to effectively maintain the first node Q(N) and the output endG(N) at low voltage level.

The boost part 300 is employed to boost the voltage level of the firstnode Q(N) in functioning period.

The first pull-down part 400 is employed to pull down the voltage levelof the first node Q(N) to the second DC constant low voltage level VSS2according to the second clock driving signal XCKN in non-functioningperiod.

The GOA circuit employs an output signal of the output end G(N) as beinga former-latter level transfer signal. The output end G(N−1) of theN−1th GOA unit which is the former stage of the Nth GOA unit and theoutput end G(N) of the Nth GOA unit are employed for performing theformer-latter level transfer which is capable of reducing the amount ofthe TFTs and realizing the objective of saving layout and powerconsumption

Please refer to FIG. 3. FIG. 3 is a circuit diagram of the GOA circuitbased on LTPS semiconductor TFT according to the second embodiment ofthe present invention. As shown in FIG. 3, the difference of the secondembodiment from the first embodiment is, the pull-down holding part 500further comprises a ninth transistor T9, and a gate of the ninthtransistor T9 is coupled to the first node Q(N), and a source iselectrically coupled to the gate of a tenth transistor T10, and a drainis electrically coupled to the third DC constant low voltage level VSS3;an eleventh transistor T11, and both a gate and a source of the eleventhtransistor T11 are electrically coupled to the DC constant high voltagelevel H, and a drain is electrically coupled to the gate of the tenthtransistor T10; the gate of the tenth transistor T10 is disconnectedwith the second node P(N). Beside this, the rest portions are the sameas the first embodiment. No redundant description is repeated here.

FIG. 4, FIG. 5 respectively are output waveform diagrams of two waveformsettings and the key nodes in a GOA circuit based on LTPS semiconductorTFT according to the present invention. The signal output waveform ofthe first node Q(N) changes according to the variation of the waveformduty ratios of the first clock driving signal CKN and the second clockdriving signal XCKN. The waveform duty ratios of the first clock drivingsignal CKN and the second clock driving signal XCKN shown in FIG. 4 aredifferent from the waveform duty ratios of the first clock drivingsignal CKN and the second clock driving signal XCKN shown in FIG. 5. InFIG. 4 and FIG. 5, CK1N, CK2N respectively represent a first line, asecond line of the first clock driving signals CKN. XCK1N, XCK2Nrespectively represent a first line, a second line of the second clockdriving signals XCKN. As shown in figures, all the waveform duty ratiosof the first clock driving signals CKN and the second clock drivingsignals XCKN are smaller than 50/50; in combination with FIG. 1, thefourteenth transistor T14 pulls down the voltage level of the first nodeQ(N) to the second DC constant low voltage level VSS2 in a high voltagelevel period of the second clock driving signal XCKN. The signal outputwaveform of the first node Q(N) appears to be convex, and the output endG(N) normally outputs.

In conclusion, in the GOA circuit based on LTPS semiconductor TFT, thepull-down holding part utilizes a high/low voltage reverse design andcomprises a first, a second and a third DC constant low voltage levelswhich are sequentially abated and a DC constant high voltage level. Theinfluence of electrical property of the LTPS semiconductor TFT to theGOA driving circuit, and particularly the bad function due to theelectric leakage issue can be solved; meanwhile, the existing issue thatthe second node voltage level and the pull-down holding circuit part inthe GOA circuit based on the LTPS semiconductor TFT cannot be at highervoltage level in the non-functioning period can be solved to effectivelymaintain the first node and the output end at low voltage level.

Above are only specific embodiments of the present invention, the scopeof the present invention is not limited to this, and to any persons whoare skilled in the art, change or replacement which is easily derivedshould be covered by the protected scope of the invention. Thus, theprotected scope of the invention should go by the subject claims.

What is claimed is:
 1. A gate drive on array (GOA) circuit based on lowtemperature polycrystalline silicon (LTPS) semiconductor thin filmtransistor (TFT), comprising a plurality of GOA units which are cascadeconnected, and N is set to be a positive integer and an Nth GOA unitcomprises a pull-up control part, a pull-up part, a first pull-down partand a pull-down holding part; the pull-up control part comprises a firsttransistor, and both a gate and a source are electrically coupled to anoutput end of an N−1th GOA unit which is the former stage of the Nth GOAunit, and a drain is electrically coupled to a first node; the pull-uppart comprises a second transistor, and a gate thereof is electricallycoupled to the first node, and a source is electrically coupled to afirst clock driving signal, and a drain is electrically coupled to anoutput end; the pull-down holding part is electrically coupled to thefirst node, the output end, a DC constant high voltage level, and afirst, a second and a third DC constant low voltage levels; thepull-down holding part utilizes a high/low voltage reverse design andcomprises: a third transistor, and both a gate and a source of the thirdtransistor are electrically coupled to the DC constant high voltagelevel, and a drain is electrically coupled to a source of a fifthtransistor; a fourth transistor, and a gate of the fourth transistor iselectrically coupled to the drain of the third transistor, and a sourceis electrically coupled to the DC constant high voltage level, and adrain is electrically coupled to a second node; the fifth transistor,and a gate of the fifth transistor is electrically coupled to the firstnode, and the source is electrically coupled to the drain of the thirdtransistor, and a drain is electrically coupled to the first DC constantlow voltage level; a sixth transistor, and a gate of the sixthtransistor is electrically coupled to the first node, and a source iselectrically coupled to the second node, and a drain is electricallycoupled to a source of an eighth transistor; the eighth transistor, andthe gate of the eighth transistor is electrically coupled to the firstnode, and the source is electrically coupled to the drain of the sixthtransistor, and a drain is electrically coupled to the third DC constantlow voltage level; the tenth transistor, and the gate of the tenthtransistor is electrically coupled to the second node and a source iselectrically coupled to the DC constant high voltage level, and a drainis electrically coupled to the drain of the sixth transistor; a twelfthtransistor, and a gate of the twelfth transistor is electrically coupledto the second node, and a drain is electrically coupled to the firstnode, and a source is electrically coupled to the second DC constant lowvoltage level; a thirteenth transistor, and a gate of the thirteenthtransistor is electrically coupled to the second node, and a drain iselectrically coupled to the output end, and a source is electricallycoupled to the first DC constant low voltage level; the thirdtransistor, the fourth transistor, the fifth transistor, the sixthtransistor, provide positive high voltage levels, employed to controlactivations of the twelfth transistor and the thirteenth transistor; theeighth transistor constructs a reverse bootstrap of negative voltagelevel in a functioning period, employed to provide a lower voltage levelto the second node in the functioning period; the DC constant highvoltage level is utilized to provide a proper high voltage level to thesecond node in a non-functioning period to maintain the first node andthe output end at low voltage level; the first pull-down part iselectrically coupled to the first node, a second clock driving signaland the second DC constant low voltage level, and the pull-down partpulls down a voltage level of the first node to the second DC constantlow voltage level according to the second clock driving signal; thefirst pull-down part comprises a fourteenth transistor, and a gate ofthe fourteenth transistor is electrically coupled to the second clockdriving signal, and a source is electrically coupled to the first node,and a drain is electrically coupled to the second DC constant lowvoltage level; the third DC constant low voltage level<the second DCconstant low voltage level<the first DC constant low voltage level. 2.The GOA circuit based on LTPS semiconductor TFT according to claim 1,wherein the pull-down holding part further comprises a ninth transistor,and a gate of the ninth transistor is coupled to the first node, and asource is electrically coupled to the gate of the tenth transistor, anda drain is electrically coupled to the third DC constant low voltagelevel; an eleventh transistor, and both a gate and a source of theeleventh transistor are electrically coupled to the DC constant highvoltage level, and a drain is electrically coupled to the gate of thetenth transistor; the gate of the tenth transistor is disconnected withthe second node.
 3. The GOA circuit based on LTPS semiconductor TFTaccording to claim 1, wherein the fourth transistor, the sixthtransistor and the eighth transistor are coupled in series.
 4. The GOAcircuit based on LTPS semiconductor TFT according to claim 1, furthercomprises a boost part, and the boost part is electrically coupledbetween the first node and the output end, employed to boost voltagelevel of the first node.
 5. The GOA circuit based on LTPS semiconductorTFT according to claim 4, wherein the boost part comprises a capacitor,and one end of the capacitor is electrically coupled to the first node,and the other end is electrically coupled to the output end.
 6. The GOAcircuit based on LTPS semiconductor TFT according to claim 1, whereinwaveform duty ratios of the first clock driving signal and the secondclock driving signal are smaller than 50/50; the fourteenth transistorpulls down the voltage level of the first node to the second DC constantlow voltage level in a high voltage level period of the second clockdriving signal.
 7. The GOA circuit based on LTPS semiconductor TFTaccording to claim 4, wherein a signal output waveform of the first nodechanges according to the variation of the waveform duty ratios of thefirst clock driving signal and the second clock driving signal.
 8. TheGOA circuit based on LTPS semiconductor TFT according to claim 7,wherein a signal output waveform of the first node appears to be convex.9. The GOA circuit based on LTPS semiconductor TFT according to claim 1,wherein in the first level connection of the GOA circuit, both the gateand the drain of the first transistor are electrically coupled to anactivation signal end of the circuit.
 10. The GOA circuit based on LTPSsemiconductor TFT according to claim 1, wherein the GOA circuit employsan output signal of the output end as being a former-latter leveltransfer signal.
 11. A gate drive on array (GOA) circuit based on lowtemperature polycrystalline silicon (LTPS) semiconductor thin filmtransistor (TFT), comprising a plurality of GOA units which are cascadeconnected, and N is set to be a positive integer and an Nth GOA unitcomprises a pull-up control part, a pull-up part, a first pull-down partand a pull-down holding part; the pull-up control part comprises a firsttransistor, and both a gate and a source thereof are electricallycoupled to an output end of an N−1th GOA unit which is the former stageof the Nth GOA unit, and a drain is electrically coupled to a firstnode; the pull-up part comprises a second transistor, and a gate of thesecond transistor is electrically coupled to the first node, and asource is electrically coupled to a first clock driving signal, and adrain is electrically coupled to an output end; the pull-down holdingpart is electrically coupled to the first node, the output end, a DCconstant high voltage level, and a first, a second and a third DCconstant low voltage levels; the pull-down holding part utilizes ahigh/low voltage reverse design and comprises: a third transistor, andboth a gate and a source of the third transistor are electricallycoupled to the DC constant high voltage level, and a drain iselectrically coupled to a source of a fifth transistor; a fourthtransistor, and a gate of the fourth transistor is electrically coupledto the drain of the third transistor, and a source is electricallycoupled to the DC constant high voltage level, and a drain iselectrically coupled to a second node; the fifth transistor, and a gateof the fifth transistor is electrically coupled to the first node, andthe source is electrically coupled to the drain of the third transistor,and a drain is electrically coupled to the first DC constant low voltagelevel; a sixth transistor, and a gate of the sixth transistor iselectrically coupled to the first node, and a source is electricallycoupled to the second node, and a drain is electrically coupled to asource of an eighth transistor; the eighth transistor, and the gate ofthe eighth transistor is electrically coupled to the first node, and thesource is electrically coupled to the drain of the sixth transistor, anda drain is electrically coupled to the third DC constant low voltagelevel; the tenth transistor, and the gate of the tenth transistor iselectrically coupled to the second node and a source is electricallycoupled to the DC constant high voltage level, and a drain iselectrically coupled to the drain of the sixth transistor; a twelfthtransistor, and a gate of the twelfth transistor is electrically coupledto the second node, and a drain is electrically coupled to the firstnode, and a source is electrically coupled to the second DC constant lowvoltage level; a thirteenth transistor, and a gate of the thirteenthtransistor is electrically coupled to the second node, and a drain iselectrically coupled to the output end, and a source is electricallycoupled to the first DC constant low voltage level; the thirdtransistor, the fourth transistor, the fifth transistor, the sixthtransistor provide positive high voltage levels, employed to controlactivations of the twelfth transistor and the thirteenth transistor; theeighth transistor constructs a reverse bootstrap of negative voltagelevel in a functioning period, employed to provide a lower voltage levelto the second node in the functioning period; the DC constant highvoltage level is utilized to provide a proper high voltage level to thesecond node in a non-functioning period to maintain the first node andthe output end at low voltage level; the first pull-down part iselectrically coupled to the first node, a second clock driving signaland the second DC constant low voltage level, and the pull-down partpulls down a voltage level of the first node to the second DC constantlow voltage level according to the second clock driving signal; thefirst pull-down part comprises a fourteenth transistor, and a gate ofthe fourteenth transistor is electrically coupled to the second clockdriving signal, and a source is electrically coupled to the first node,and a drain is electrically coupled to the second DC constant lowvoltage level; the third DC constant low voltage level<the second DCconstant low voltage level<the first DC constant low voltage level; theGOA circuit further comprises a boost part, and the boost part iselectrically coupled between the first node and the output end, employedto boost voltage level of the first node; wherein the boost partcomprises a capacitor, and one end of the capacitor is electricallycoupled to the first node, and the other end is electrically coupled tothe output end; wherein waveform duty ratios of the first clock drivingsignal and the second clock driving signal are smaller than 50/50; thefourteenth transistor pulls down the voltage level of the first node tothe second DC constant low voltage level in a high voltage level periodof the second clock driving signal; wherein a signal output waveform ofthe first node appears to be convex.